1. Field of the Invention
The present invention relates to a hollow golf club head in which the vibration characteristics of a face portion, a crown portion and a sole portion are controlled to optimize the carry and the hit ball sound.
2. Description of the Related Art
Conventional, it has been proposed that the vibration characteristics of a golf club head are controlled to improve the performance (shot sound and bounce) of the golf club head.
For example, JP-A-2005-6763 discloses a design method for a golf club head, including a step of primarily designing the golf club head, a step of acquiring the vibration characteristics for the golf club head through the mode analysis on a computer, a step of manufacturing the golf club head experimentally and sampling the hit ball sound, a step of specifying the improvements for improving the hit ball sound based on the hit ball sound and the vibration characteristics, and a step of secondarily designing the golf club head by applying the above improvements.
JP-A-2004-135858 discloses a metallic hollow golf club head of wood type in which the ratio of the primary natural frequency of the face portion to the primary natural frequency of the sole portion is from 0.95 to 1.05 in the characteristic vibration measurement by a centrally supporting stationary excitation method employing an electromagnetic excitation unit or a suspension blow excitation method employing an impulse hammer.
JP-A-2003-339919 discloses a golf club head in which the primary fixed natural frequency of a golf club head in a state where the central part of the face portion is restrained is from 500 Hz to 900 Hz, and the primary free natural frequency of the golf club head in an unrestrained state is from 3000 Hz to 5000 Hz.
JP-A-2002-17904 discloses a golf club head in which the natural frequency of the head portion to be measured at a sweet spot is smaller than the natural frequency of the golf ball.
Conventionally, it is common practice that the face portion is made less elastic by measuring the vibration of only the face portion, and setting the primary frequency (primary natural frequency) of the face portion to a low frequency, whereby increasing the initial velocity of the hit ball.